Choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD) is the leading cause of blindness among Americans aged 65 and over. Laser photocoagulation, the only proven treatment, is applicable to only a small subset of eyes with CNV. Even with laser treatment, the average final visual acuity is 20/250-20/320. There are no proven treatments for prevention of (CNV) secondary to AMD. Since the first report of the use of external beam radiation for the treatment of CNV, the results of many uncontrolled case series have been reported and the procedure has been adopted as a standard treatment in some areas. Due to the large segment of the population that might benefit, or be harmed, by radiation treatment, a controlled randomized study of radiation therapy is warranted. In this application, we request support for the planning of a multicenter clinical trial, the Age-related Macular Degeneration and Radiation Trial (AMDRT), to assess the safety and effectiveness of radiation treatment in preventing the loss of visual function due to CNV. The specific aims of the multicenter, randomized clinical trial are to: 1. Evaluate radiation treatment for previously untreated subfoveal neovascularization secondary to age-related mucular degeneration (New Subfoveal CNV Substudy); 2. Evaluate radiation treatment for CNV lesions which have been treated with laser but show leakage on fluorescein angiography (Recurrent CNVSubstudy); 3. Evaluate adjuvant radiation treatment to prevent visual acuity loss from recurrent CNV in patients treated with laser photocoagulation (Recurrence Prevention Substudy). The specific aims to be accomplished during the time period covered by this application are to: 1. Further refine the design of the AMDRT, with particular attention to the feasibility of sham treatment and the short-term side effects of the proposed dose of radiation; 2. Prepare a complete manual of operations for the AMDRT; 3. Refine procedures for the AMDRT Coordinating Center, Reading Centers, and Radiological Physics Center; 4. Prepare grant applications for the AMDRT central resource centers and clinical centers.